The present invention relates to a sight for an archery bow and, more particularly, to a sight of relatively simple construction and operation which is adjustable for varying sight distances.
The prior art is replete with bow sights which are adjustable to cause the sight element to move vertically with changes in the target distance to alter the trajectory of the arrow. In many of these adjustable sights, a distance scale indicator allows the archer to move a distance indicator to coincide with the estimated target distance. Movement of the indicator automatically moves the sight element so that the bow will be appropriately tilted to provide the necessary trajectory. A number of prior art device utilize a quadrilateral or four-leg linkage to which both the distance pointer and sight element are attached The legs of the quadrilateral linkage, which may include portions of the mounting structure, are generally of unequal lengths such that incremental movement of the distance indicator will be translated through the linkage and result in some other incremental movement of the sight element. Adjustable sights of this type are shown, for example, in U.S. Pat. Nos. 4,418,479; 4,497,116; and 4,541,179. A similar sight construction, but one not having a distance indicator, is shown in U.S. Pat. No. 4,109,390.
Sights utilizing a quadrilateral linkage to impart complimentary movement to the distance indicator and sight element are generally of two types. In one type, equal incremental movements of the sight distance indicator toward increasing target distance positions causes progressively greater incremental movements of the sight element. This type of arrangement is shown in previously identified U.S. Pat. Nos. 4,418,479 and 4,541,179. In the quadrilateral sight adjustment linkage in U.S. Pat. No. 4,497,116, progressively increasing incremental movements of the sight distance pointer result in proportionally greater incremental movements of the sight element as well. A similar movement of the sight occurs in the device shown in U.S. Pat. No. 4,109,390, although as indicated previously, the trigger mechanism does not include a distance indicator. All of the foregoing patents, however, recognize the principle that with equal incremental increases in the target distance, the arrow must be tilted through progressively increasing vertical angles to provide the necessary increase in trajectory to compensate for the increasing effect of gravity on the flight of the arrow. In a somewhat more simple adjustable sight construction, U.S. Pat. No. 2,667,692 discloses a device which provides a sight indicator that compensates both for the necessary progressive increase in the vertical angle and for varying bow strengths.
Those prior art devices which utilize quadrilateral linkages to interconnect the distance indicator and sight element are characterized by their complex constructions, including a large number of parts and four or more separate pivotal connections. It has been found, however, that such complex arrangements by which certain incremental movements of the sight distance indicator result in some type of proportional incremental movement of the sight element do not accommodate the use of a standard preset scale for distance indication. Rather, depending on the type and strength of the bow and possibly other factors, archers ordinarily use a "shoot and try" method of sight calibration in which the yard markers are set by a simple process of repeated shooting at incremental distances (e.g. 10 yards), marking the distance scale at the position of the distance indicator when on target, repeating the procedure at increasing 10 yard increments from the target, and applying the incremental distance marks to the distance scale. In other words, the distance indications on the bow sight distance scale are usually uniquely positioned for each bow and for the archer using it. Another problem exhibited by bow sights with pivotal multi-leg linkages is the tendency of the sight to be thrown off the set sight distance as a result of the "kick" caused by the arrow as it is released.
Somewhat simpler adjustable bow sight constructions are shown in U.S. Pat. Nos. 2,642,661 and 3,318,298 in each of which the sight element slides in a generally vertically disposed track to provide adjustment corresponding to varying target distances. In both of these sights, incremental movement of the sight along the distance indicator results in directly equal movement of the sight element.
Although the prior art sights identified above have performed adequately, there is a need for a simplified construction which will provide the same basic operation and is easy to adjust and use. The sight should also be of rugged construction and adaptable for use on wide ranges of bow types.